The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to structures for switches and methods for forming structures that include a switch.
Complementary metal-oxide semiconductor (CMOS) circuitry is utilized in mobile communication devices (e.g., laptops, cellular phones, tablets, etc.) to handle wireless high frequency signals transmitted to and/or received by the mobile communication devices. The circuitry may include a low noise amplifier and a high frequency switch that allows for high frequency signals received by an antenna to be routed from the low noise amplifier to other chip circuitry and for high frequency signals to be routed from a power amplifier to the antenna. The high frequency switch may include a stack or bank of field-effect transistors formed by CMOS processes. Field-effect transistors fabricated on a bulk wafer may exhibit poor linearity due to, for example, non-linear electric fields on the substrate and poor intermodulation properties. Semiconductor-on-insulator (SOI) wafers may mitigate some of these issues, but are costly in comparison with bulk wafers.
The field-effect transistors of a high-voltage switch may be stacked to withstand the switching of voltages that are greater than the breakdown voltages of the individual field-effect transistors. The field-effect transistors of a high-voltage switch fabricated using the device layer of an SOI wafer are isolated by the buried oxide layer from the substrate. However, such electrical isolation is absent when the stacked field-effect transistors of a high-voltage switch are fabricated using a bulk wafer.
Improved structures for switches and methods for forming structures that include a switch are needed.